Communications between computers, peripheral devices, Internet appliances and other network devices increasingly require higher data transfer rates to handle multimedia and other rich content. Communication media such as twisted pair cable, fiber and wireless links with increased data carrying capacity are now being used to meet the increased data carrying demands.
The network devices have varying communication abilities and may use different types of media. For example, a first network device or link partner may be able to communicate wirelessly with a second link partner at a first rate such as 10 Megabits per second (Mbps). A third network device or link partner may communicate with a fourth link partner at Gigabit per second rates over fiber. A fifth network device or link partner may communicate over copper media with a sixth link partner at Gigabit or sub-Gigabit speeds. Because of the variable types of media that are used and the different communication speeds, accommodation must be made for situations where the prospective link partners have different communication abilities.
The physical layer device (PHY) of some network devices includes an autonegotiation circuit, which initiates an exchange of information between two link partners. The autonegotiation circuit automatically configures the link partners to take maximum advantage of their respective abilities. During auto-negotiation, the link partners advertise their abilities using configuration code groups, acknowledge receipt, identify common modes of operation, and reject the use of operational modes that are not shared or supported by both link partners. When more than one common mode of operation exists between the network devices, an arbitration function of the autonegotiation circuit identifies and selects a single mode of operation. After auto-negotiation is complete, the devices establish a link and exchange data.
Auto-negotiation on some media types such as fiber requires that both of the link partners support auto-negotiation functionality before a link between the link partners can be automatically established. If one link partner implements auto-negotiation and the other link partner does not, two-way communications cannot be established without manual intervention. A user must disable auto-negotiation and manually configure both link partners to work in the same operational modes.